Substances

The consequences of natech events mainly depend on the quantity and characteristics of the substances involved in the event and their storage conditions. Certain consequences are only possible for selected substances. For example, fire is probable only if the released substance is flammable. The nature of dis-persion of a gaseous substance depends - among other factors - on its molecular weight. For liquid substances, the amount that will be dispersed is a function of boiling point and vapor pressure. The concen-tration, which results in a certain level of adverse effect on human health or environment, also differs from substance to substance. Therefore, besides natural hazard and plant unit properties, the consideration of substance properties is a necessity for the assessment of natech risks. For this purpose, RAPID-N features a substance database that includes information on the physical and chemical properties of substances. Substance records are used to store these data. The data fields of the substance records are listed in Table 1.

Table 1. Substance data fields

Basic information stored in the system on substances includes name, identifier and structure data (Figure 1). Multilingual substance names may contain Greek symbols. Italic, subscript and superscript formatting supported as well. If a substance has multiple names according to different naming conventions and notations, they can be entered by using semi-colon as separator.

Since substance names are not unique and difficulties exist in finding a substance solely from its name, frequently used chemical identifiers are included to the substance information. Available identifiers are:

• Chemical Abstracts Service Registry No of the American Chemical Society (CAS),
• European Inventory of Existing Chemical Substances (EINECS), and European List of Notified Chemical Substances (ELINCS) No of the European Union (EC No),
• 67/548/EEC Directive Annex I Index No (EC Index No).

The CAS number is mandatory for each substance. Information on the structure of the substance is stored as chemical formula and compact linear strings in International Chemical Identifier (InChI) (Stein et al., 2003) and Simplified Molecular Input Line Entry Specification (SMILES) (Weininger, 1988) nota-tions. Besides giving insight into the chemical structure of the substance, these identifiers can also be used to estimate chemical properties by using structure-property relationships. This possibility will be explored in the next versions of the RAPID-N.

The properties of substances can also be indicated by using the generic property definition mechanism of the system. Similar to other records, property values in standard units are automatically calculated for numerical properties. Missing property data can be estimated by using property estimators if suffi-cient data is available (Figure 6.2). Currently, there are two types of substance properties used for risk assessment calculations. The first type is common physical and chemical properties, such as molecular weight and boiling point. The second type is specific to the consequence calculations by using U.S. EPA’s RMP Guidance for Offsite Consequence Analysis methodology and includes toxic endpoints, nature of the released plume, and substance-specific factors to facilitate computations. See Table 4.12 for the list of supported substance properties with short descriptions.